This invention relates to a jounce bumper for motor vehicle suspensions systems either in the strut assemblies or other locations.
Microcellular urethane bumpers are used in vehicle suspensions to absorb energy during jounce and to act as a supplemental spring. These could be mounted on a strut assembly, as own in the U.S. Pat. No. 5,487,535, where the bumper surrounds the piston rod of the strut. This bumper prevents the cylinder of the strut assembly from impacting heavily the mounting assembly. The bumpers could also be mounted in other locations, as shown in U.S. Pat. No. 5,725,203, where the bumper is free standing to prevent a control arm of the suspension from impacting with the vehicle frame.
Bumpers can be mounted in a free state or within a rigid cup. U.S. Pat. No. 6,158,726 discloses a bumper with the use of a rigid cup attached. The rigid cup acts to attach the bumper to the vehicle or the strut and limits the bumper distortion, thereby increasing its rate. The force necessary to compress the bumper increases as the bumper is compressed and the bumper absorbs energy as it is compressing. As the bumper is compressed, the resistance to compression increases to the point where the bumper acts as a solid, and transfers the remaining energy from the impact to the vehicle. The use of a rigid cup or another constraint limits the bulging of the bumper, thereby reducing the amount of travel needed to reach the point where the bumper becomes a solid.
In general, when more energy must be removed, a larger bumper is used. Recent styling trends are dictating the use of low profile tires, which in effect removes an important energy management element. To counteract the loss of the cushioning given by higher profile tires, the jounce bumpers must absorb much greater amounts of energy. In most cases, there is not enough space to package a bumper large enough to absorb the amount of energy experience during an impact.
One object of the invention is to provide a bumper assembly which overcomes the limiting effect a rigid cup has on a bumper assembly. Another object of the invention is to provide a compact bumper assembly capable of absorbing a larger amount of energy than a similar sized bumper assembly, and provide more travel of the strut assembly.
These and other problems are overcome by a bumper assembly comprising a microcellular urethane (MCU) jounce bumper placed into a thermoplastic urethane (TPU) cup. The MCU bumper is partially placed within the TPU cup, which is attached to a surface of either a strut assembly or is free standing in another assembly. As a force acts upon the MCU bumper, it begins to press into the TPU cup. Upon an increasing force being applied, the TPU cup begins to expand outwardly at its opening at the same time the MCU bumper compresses within the TPU cup. Thus, the combination of the bumper and the cup act in unison to receive the force, and allow more travel of the strut assembly as the cup expands. As a result, the combination bumper assembly is capable of absorbing an increased amount of energy in a compact area while still allowing more travel of the strut assembly.